Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $54.96   8.617%   $59.6959   $59.70   $59.70   $59.70  
  Purchase #2 $145.87   9.119%   $159.1719   $159.17   $159.15   $159.20  
  Purchase #3 $31.79   9.207%   $34.7169   $34.72   $34.70   $34.70  
  Purchase #4 $225.35   6.867%   $240.8248   $240.82   $240.80   $240.80  
  Purchase #5 $161.27   9.135%   $176.002   $176.00   $176.00   $176.00  
  Purchase #6 $163.61   12.402%   $183.9009   $183.90   $183.90   $183.90  
  Purchase #7 $126.32   4.643%   $132.185   $132.19   $132.20   $132.20  
  7 purchase totals = $909.17       $986.4974   $986.50   $986.45   $986.50